Various systems for locating are already known.
EP 0 512 789 shows a locating system of high accuracy which utilizes the global positioning system (GPS) for determining position, speed and time information for, for example, a vehicle in a mobile radio system. To increase the accuracy in position determination, reference measurements can be made at known locations. These reference measurements are utilized for increasing the locating accuracy in the areas around these locations. The system also has the possibility of storing a digital map of the area in question and utilizing this for facilitating the position calculations.
EP 0 335 558 describes a radio communications system with fixed and mobile stations. The mobile stations can be located by measuring the transit time for signals between the mobile stations and at least two fixed stations. The accuracy of the system can be improved by storing data which represent a route map of the area in question in the base stations. The calculated position can then be adjusted in accordance with the map by assuming that the mobile station is located on a road.
U.S. Pat. No. 5,166,694 describes a system for locating vehicles. The system is provided with good accuracy by utilizing all the information which is available in the fixed receivers. The system then selects an optimum array of information which provides the smallest error and uses this array for calculating the position. The calculation time can be shortened by only using part of the available information.
U.S. Pat. No. 5,043,736 relates to a cellular telephone system with the possibility of obtaining the current position of a person in the system. The mobile station, which is located with the aid of satellites, transmits information about its position to the cellular telephone system. The position of the mobile station can be centrally monitored with the aid of this information.
EP 0 431 956 shows a way of monitoring a mobile telephone system. The system has the possibility of receiving, via the base stations, data such as position, signal quality and signal strength for a mobile during an ongoing call. This information can then be presented visually in such a manner that it is easy to follow where the traffic is being generated and what coverage there is in the system.
The present invention permits a further improvement of the accuracy in locating by using an adaptive neural network which is trained with reference data and measurement data from mobile stations. The accuracy is high, especially in comparison with earlier systems which only utilize the timing advance (TA) information which can give considerable errors due to time dispersion.